The present invention relates to an electronically controlled hydraulic brake system which increases a brake hydraulic pressure by supplying brake fluid into a brake hydraulic pressure line by means of an electronically controlled pressure increasing pump, and more particularly to a method of controlling a drive current command value of a motor for the pressure increasing pump so as to linearly compensate a non-linear characteristic of the brake hydraulic pressure.
Japanese Published Patent Application No. 2001-301592 discloses an electronic control system for a pump drive motor in an electronically controlled hydraulic brake system shown in FIG. 10. This electronic control system is arranged to obtain a demand motor output (feedforward controlled variable) Ws by multiplying a rate dPmc/dt of change (changing speed) of a master cylinder hydraulic pressure (brake hydraulic pressure command value) Pmc and a coefficient C1 according to the rate of change of an actual brake (wheel cylinder) hydraulic pressure, to obtain an increasing quantity δPws due to demand motor output Ws by multiplying the demand motor output Ws and a constant C2, to obtain a brake hydraulic pressure estimated value Pes by adding actual brake (wheel cylinder) hydraulic pressure Pwc to the obtained increasing quantity δPws, and to obtain a motor output feedback controlled variable ΔW necessary for eliminating a brake hydraulic pressure difference ΔP by executing a feedback calculation such as a PID control according to a difference ΔP between break hydraulic pressure estimated value Pes and brake hydraulic pressure command value (master cylinder hydraulic pressure) Pmc. Further, the brake control system is arranged to control the motor by setting a target motor output at a sum of demand motor output (feedforward controlled variable) Ws and motor output feedback controlled variable ΔW so as to obtain the desired output.